1. Field of the Invention
The present invention relates to a road shape predicting method for predicting the road shape on the basis of map data which are a collection of a plurality of nodes, and a vehicle controlling method using such a predicting method.
2. Description of the Related Art
Such a road shape predicting method and a vehicle controlling method were proposed in U.S. patent application Ser. No. 09/056,244 by the applicant of this invention. As seen from FIG. 4, they use coordinates of a larger number of nodes N.sub.N (N.sub.N =N.sub.0, N.sub.1, N.sub.2, N.sub.3, . . . ) set at prescribed intervals on a road as road map data. On the basis of a link length L.sub.N which is defined as a distance between adjacent nodes N.sub.N and N.sub.N+1, and a crossing angle .theta..sub.N formed by a certain link N.sub.N-1 N.sub.N and another link N.sub.N N.sub.N+1 located forward, a passing state decision quantity (vehicle cornering amount) .theta..sub.N /L.sub.N at each node is computed. The passable speed at the node N.sub.N computed on the basis of the passing state decision quantity .theta..sub.N /L.sub.N is compared with the passage predicting speed at the node N.sub.N through which an own vehicle passes. If it is decided that the passage is difficult, a warning is given to a driver or automatic speed reduction is made. The above passing state decision quantity .theta..sub.N /L.sub.N corresponds to a change quantity in the azimuth angle of a vehicle for a moving distance thereof. Its large value indicates that the road is curved, whereas its small value indicates that the road is straight.
Where there are three nodes N.sub.0, N.sub.1, N.sub.2, on a straight road as shown in FIG. 9, if the positions of the nodes are deviated from the inherent N.sub.0, N.sub.1, N.sub.2, to N.sub.0 ', N.sub.1 ', N.sub.2 ', owing to an error in the road map data, at the node N.sub.1, the passing state quantity .theta.1/L1 which should not be essentially produced is produced. In this case, if the link length L.sub.1 between N.sub.1 and N.sub.2 is sufficiently large, the passing state decision quantity .theta..sub.1 /L.sub.1 is relatively small so that the road shape is decided to be a gentle curve approximately to the straight road. Thus, no hitch occurs. On the other hand, if the link length L.sub.1 between N.sub.1 and N.sub.2 is small, the passing state quantity .theta..sub.1 /L.sub.1 is fairly large so that the road shape which should be actually straight is decided to be erroneously curve.